How to use try/catch in Swift to handle exceptions

The try/catch syntax was added in Swift 2.0 to make exception handling clearer and safer. It's made up of three parts: do starts a block of code that might fail, catch is where execution gets transferred if any errors occur, and any function calls that might fail need to be called using try.

Here's a working example that loads an input.txt file from the app bundle into a string:

Note the exclamation mark: try!. This means "I realize this call might throw an exception, but trust me: it never, ever will." This is useful only if you're 100% sure the call is safe. In our example we're loading a file from the app bundle, and if that file isn't there it means our app is corrupted, so it's OK to use here. You don't need do/catch when you use try!.

The second option is try? which means "if this call throws an exception, just return nil instead." This is closer to the Objective-C way of handling errors, which was a bit scruffy. If this is your preferred way of handling errors, then go for it! You don't need do/catch when use try?, but you should check and unwrap the result carefully.

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